This is not a difficult fix. In the bottom left corner of your dashboard screen you can set the resolution to an exact setting. Current I'd suspect you are on Range or on Automatic. These should be set to the exact resolution that you wish others to consume and use the dashboard. Alternatively there's also a way around doing this using blank objects and using layout containers.https://www.interworks.com/blog/tspaulding/2013/08/07/understanding-layout-containers-tableau this should help you get a good grasp of how to use these to your advantage.

This is not accurate. You're able to select your dashboard resolution per pixel from a dashboard. I rarely if ever use range and will oft set this to exactly. I will also use desktop, etc. Whatever fits my clients needs. Hopefully you're able to use this.

When you select the drop down next to desktop you get automatically, exact, range and then about 15 or so other popular resolutions.